What are the injection molding processes that affect the strength of injection molded parts


1. Hot oil injection molding can improve the strength o […]

1. Hot oil injection molding can improve the strength of steel parts and nylon parts
Nylon and POM materials are all crystalline plastics. The mold is injected with hot oil by a hot oil machine, which can slow down the cooling rate of the injection molded part and improve the crystallinity of the plastic. At the same time, due to the slowing down of the cooling rate, the residual internal stress of the injection molded part is also reduced. Therefore, the impact resistance and tensile strength of nylon and POM parts injected with hot oil in a hot oil machine will be improved accordingly.
It should be noted that the size of nylon and POM parts injected with hot oil in a hot oil machine is somewhat different from that of injection molded parts with water, and nylon parts may be larger.

2. The melting speed is too fast, even if the injection temperature is 180℃, the glue will be raw
Normally, PVC 90°C material is injection molded at 180°C, and the temperature is sufficient, so there is generally no problem of raw rubber. However, it is often due to reasons that have not attracted the attention of the operator, or deliberately speeding up the melt speed in order to speed up production, which makes the screw retreat quite fast. For example, it only takes two or three seconds to retract the screw to the maximum melt volume. At more than one part of the position, the time for the PVC material to be heated and stirred is seriously insufficient, causing the melt temperature and uneven mixing of the raw rubber, which makes the strength and toughness of the injection molded part quite poor.
Therefore, when injecting PVC materials, be careful not to adjust the speed of the melt to more than 100 rpm. If you must adjust it very quickly, remember to increase the temperature of the material by 5 to 10°C, or increase the back pressure of the melt to match. At the same time, you must always check whether there is any problem with the raw rubber, otherwise it is very likely to be Cause heavy losses.

3. Increasing the injection pressure can increase the tensile strength of PP injection molded parts
Compared with other hard rubber materials, PP material is more elastic, so the density of injection molded parts will increase with the increase of pressure. This characteristic is relatively obvious. When the density of a plastic part increases, its tensile strength will naturally increase, and vice versa.
However, when the density increases to the maximum that PP itself can reach, and then increase the pressure, the tensile strength will not continue to increase, but will increase the residual internal stress of the injection molded part, making the injection molded part brittle, so it should be adequate.